The Pediatric HIV AIDS Cohort Study addresses two critical research questions: (1) the consequences of fetal and infant exposure to antiretroviral therapy (ART) when used to prevent mother-to-child transmission of HIV-1, and (2) the clinical course of perinatal HIV infection among children as they proceed through adolescence towards adulthood. These questions are being addressed through two separate protocols being conducted at multiple sites in the US and Puerto Rico. The specific aim of the SMARTT Study is, among HIV-exposed infants, to define the short and long-term safety of ART exposure. To accomplish this, HIV-uninfected children born to infected mothers are evaluated prospectively for growth, neurodevelopment, cardiac and other end-organ function. Children with abnormalities will be further evaluated to determine if they result from ART toxicity, with particular emphasis on mitochondrial dysfunction. The specific aims of AMP are, among a cohort of pre-adolescents and adolescents with perinatal HIV (1) to define the impact of HIV infection and ART on: growth and development; sexual maturation; pubertal development; development of risk factors for cardiovascular disease; cognitive, academic, vocational, sexual, and social functioning; mental health; and risk taking behavior including substance use. (2) to identify infectious and non-infectious complication of HIV disease and ART therapy, including end organ disease (neurologic, renal, pulmonary, bone) and nutritional and metabolic abnormalities. (3) to study genetic, epigenetic, virologic (including antiretroviral resistance), and immunologic factors which impact the course of HIV infection, its complications and response to treatment. In both protocols, subjects and their primary caregivers are prospectively evaluated according to a standardized protocol. Both utilize a strategy of triggered evaluations, with specific abnormal findings leading to additional evaluations to characterize the abnormality. Repository specimens are collected for further biochemical and genetic testing.